Apparatuses, such as a copier, a printer, an automated teller machine (ATM), a banknote processor, and a postal article processor, deal with paper sheets (or paper-like media), such as printing papers, banknotes, copy papers, post cards, envelopes, and stock notes. These apparatuses are required to extract one paper sheet after another from a stack of paper sheets. Therefore, these apparatuses each include a separation and extraction apparatus which separates a paper sheet from a stack of paper sheets and extract the paper sheet from the stack.
The separation and extraction apparatus needs to precisely extract one paper sheet after another from a stack of paper sheets without extracting multiple paper sheets. Conventionally, in order to separate and extract a paper sheet, a stack is loosened by blowing air at a side surface of the stack (also called the sheet bundle). However, for use in an automated teller machine, the separation and extraction apparatus needs to handle, for example, a stack of brand-new banknotes in which paper sheets are placed in firm contact with each other, a stack of circulated banknotes which are creased, wrinkled, and soft, and a stack of these banknotes which are stacked on and mixed with each other. Therefore, in order to steadily separate and extract one after another from such a stack of banknotes, for example, the stack needs to be handled adequately by controlling a flow rate and a pressure of the blown air, depending on the bundle state of the stack.
Further, JP-A 2007-145567 (Patent Document 1) discloses a separation and extraction apparatus in which a vibration unit is put in contact with an upper surface of a stack and a contact force between one another of paper sheets is reduced by vibrating the stack, to extract one paper sheet after another. In such a separation and extraction apparatus, the paper sheets each are extracted with friction sufficiently reduced between an uppermost paper sheet in the stack and another paper sheet just below the uppermost paper sheet by utilizing high-frequency vibration. Extraction of multiple paper sheets (i.e., a multiple feed) is thus prevented. Another separation and extraction apparatus which also utilizes high-frequency vibration is of a type in which the high-frequency vibration triggers separation of paper sheets. In this state, air is blown at a side surface of a stack of the paper sheets to improve extraction performance.
However, the separation and extraction apparatus disclosed in Patent Document 1 can not much improve the extraction performance if paper sheets in a stack are originally not in firm contact with one another, like a stack of wrinkled or creased paper sheets stacked on one another. The separation and extraction apparatus may rather cause a risk that paper sheets are damaged by extracting at a high speed with a tip end of the vibration unit stuck on the paper sheets.
Accordingly, a bundle-state detection apparatus which is capable of detecting a bundle state of a stack of paper sheets is demanded. Further, a separation and extraction apparatus including such a bundle-state detection apparatus is demanded to stably extract one paper sheet after another.